My invention relates to a special-purpose clutch for permitting a driven member to rotate at speed different from that of a drive member. The clutch according to my invention is suitable for use, for example, in rotary hot-stamping apparatus of the type described and claimed in my separate application cross-referenced above, the contents of which are incorporated herein insofar as is necessary for a full understanding of the invention.
In rotary hot-stamping apparatus of the type under consideration, a printing ribbon extending from payoff reel to takeup reel is placed in superposition on a continuous strip of plastics, paper or other material being fed at constant speed over a platen which may be in the form of a rotary cylinder. Type having a relief character or characters formed on its face is mounted on a rotary type carrier over the platen and is heated by a heater housed in the carrier. As the type carrier is rotated by a drive mechanism, usually including an electric motor, the heated type is periodically pressed against the printing ribbon in superposition on the strip of desired material traveling over the platen, thereby imprinting the character or characters on the strip at constant spacings.
The rotary hot-stamping apparatus of the above outlined type has the advantages, over reciprocating-type apparatus, of high speed operation and absolutely wasteless use of the printing ribbon. This type of apparatus has a problem, however, arising from the fact that the type is revolving while being pressed against the superposed ribbon and strip, which are themselves traveling over the platen, for imprinting characters on the strip. For making clear-out imprints, the angular speed of the type must be in precise agreement with the linear speed at which the strip is fed over the platen. The true utility of the rotary hot-stamping apparatus cannot be established unless a practical solution to this problem is developed.